Silver ring around 'iPhone 5S' home button may be integral to fingerprint reader, not just for looks

Reports on Friday spurred talk of a "silver ring" that will supposedly adorn the "iPhone 5S" home button, though a look at the technology driving Apple's AuthenTec sensors suggests the part is more important than just window dressing.

Apple is widely expected to launch a next-generation "iPhone 5S" at a Sept. 10 media event, with rumors and parts leaks pointing to the inclusion of a fingerprint sensor embedded in the device's home button.

While numerous reports have tried to guess what purpose the biometric sensor will serve, other than obvious security functions, and how it will work, few have investigated the technology itself. Doing so not only yields clues into possible use scenarios, but answers usability and design questions. Like those regarding the silver ring.

Clayton Morris of Fox News first mentioned the supposed shiny home button flourish last month on an episode of This Week in Tech, better known as TWiT. Morris proposed the ring is merely aesthetic, possibly added so users can easily distinguish an iPhone that has a built-in fingerprint sensor from those that do not.

However, taking a look at previous patent filings unearthed by AppleInsider, the metallic ring may be a functional component necessary to the sensor's operation.

There stands a variety of ways to accomplish biometric fingerprint readings, including the stereotypical "swiping" motion made famous in movies, as well as methods using optical, thermal, pressure and capacitive measurements, among others. AuthenTec, which Apple purchased in 2012 for $356 million, uses a few different capture methods in its products, though the tech most likely to be used in the iPhone doesn't involve swiping.

Typical methods of swipe authentication, usually direct capacitance, involve a thin "strip" sensor that captures and stitches together multiple images of a fingerprint as a user sweeps their finger across the sensing plate. With direct capacitance, an electrical field is applied to the sensor, which detects ridges and valleys ? the skin structures that form fingerprint whorls ? by measuring variations in capacitance at the sensor plate. Lower capacitance denotes skin that is farther from the sensor, or valleys, while higher capacitance is associated with ridges.

Cross section of AuthenTec's Smart Sensor with RF field technology.

A more accurate and robust method of capture is called radio frequency field sensing, or AC capacitance. Like direct capacitive sensing, this technique also measures capacitance of a sort, but the similarities end there. Instead of measuring the effect on an electrical field, a low frequency RF signal is inserted into the finger and received by the sensor. In this case, RF signal strength captured by the pixel traces are measured and the corresponding data is translated to form an image of the print.

Benefits of RF field/AC capacitance sensing include static non-swipe readings, resistance to dust and capability for the sensor to operate even when covered by layers of protective material. These types of sensors are usually larger in size to allow for a wider capture area.

One patent, filed by AuthenTec cofounder Dale R. Setlak and subsequently assigned to Apple, goes into detail about a technology based on mechanics which are very similar to RF field sensing. The property also relates to the company's "Smart Sensor" ? also based on RF field sensing tech ? which has been used successfully in at least one phone, the Japan-only Toshiba REGZA T-01D.

As noted in Setlak's patent, along with other similar inventions credited to his name, electrodes need to be in contact with the finger to pump the drive signal that will ultimately be measured by pixel traces on the pixel plate.

In nearly all RF field sensors, a ring disposed around the sensor array acts as the electrode that drives the low frequency RF signal into the finger, which is attenuated by ridges and valleys in the print and finally captured by AC sensors as a high quality image.

Illustration from Setlak's patent showing a pixel trace sensor array.

As a type of bonus side effect, the tech can also be used as a form of input. By analyzing slight movements or changes in attenuation over time, the system can interpolate gesture behaviors like scrolling, cursor control and, when combined with a physical or virtual button, drag-and-drop operations.

Embedding this type of package in an iPhone's home button is likely quite challenging as the part moves up and down constantly, which would put undue wear on the sensing module's interconnects. It is possible that Apple has found a way to separate the finger ring from the sensor array in order to isolate the integral components from wear and tear. Such a system would also be less apt to fouling or misreadings due to debris.

As for utility, the sensor design wouldn't force users to swipe the home button to authenticate, but would have the module read the print while a user presses the button to wake the phone from sleep. In other words, the security factor would take place seamlessly. No new gestures to learn, just enhanced functionality, transparent to the user.

It remains wholly unknown if Apple has incorporated this particular fingerprint technology into the next-gen iPhone, though circumstantial evidence seems to point in that very specific direction.

Further, a non-functional aesthetic bezel rimming the home button, which has seen nary a design tweak since the first iPhone launched in 2007, simply to demarcate new biometric capabilities seems to go against Apple's design sensibilities. When the company introduced a front-facing camera with the iPhone 4, it buried the feature just above the earpiece. No special decorations or embellishments to note that the handset sported FaceTime capabilities.

In any case, all should be revealed at Apple's Sept. 10 special event, at which the company is widely expected to unveil a next-generation iPhone. With or without a fingerprint sensor.

Further, a non-functional aesthetic bezel rimming the home button, which has seen nary a design tweak since the first iPhone launched in 2007, simply to demarcate new biometric capabilities seems to go against Apple's design sensibilities.

I agree, they never just stick things on for appearances, there's always a purpose behind each part.

If the fingerprint sensor works successfully watch every Android smartphone manufacturer attempt to duplicate it. I hope Apple patented everything that has to do with the software controlling the fingerprint sensor. As it is, Samsung will simply reverse-engineer the sensor and come up with a better and cheaper sensor like they do with every other piece of hardware they get their hands on. This fingerprint scanner will be claimed by the pundits that it's not innovative enough because other companies like Motorola have already attempted it and failed.

As a type of bonus side effect, the tech can also be used as a form of input. By analysing slight movements or changes in attenuation over time, the system can interpolate gesture behaviours like scrolling, cursor control and, when combined with a physical or virtual button, drag-and-drop operations.

Really well-written article. Much more balanced than Daniel Eran Dilger.

I agree with the first sentence. The second shows that you, along with many others here, don't get Dilger's M.O. He isn't motivated by the nuts and bolts of the technology so much, but the grand machinations, especially where there's conflict involved. Apple's existential struggle, and all that.

You won't see Gruber trekking down to Maiden N.C. to see the data center going up, for example. Or Philip Elmer-DeWitt checking out the demolition of the HP buildings in Cupertino. Every writer has his interests and his demons, the question being do we learn something useful from them.

Then again, I've sometimes thought that Mikey Campbell is an alter ego of Daniel Eran Dilger.Edited by Flaneur - 9/7/13 at 7:28am

Only pictures of the proposed Finger Print Scanner button are from website run by Sonny Dickson. For those that have heard his interviews on TV or have visited his website it's obvious that this is not a real part. When asked if Apple has contacted him about what he is doing he said "NO". If these were real parts I think Apple would have already done something. This guy is operating an advertising hit website making $2000 a month by providing parts that are not necessarily Apples. The more notariety be gets the more hits the bigger his profit
Take what you read on his website with a grain of salt as the credibility is lacking
By the way the 2 iPhone 5s gold and graphite cases had been out for days before he posted those parts on his website

Very interesting. If this is right, then it shows starkly how hard doubling down on secrecy really is for Apple. Then there is the whole challenge of lining up partner support for any NFC-based transaction processing. It's unlike Apple not to have this in place before announcing a major new feature. But it's been a long time since they have kept under secret any negotiations with new partners.

I'm still wondering if this will be integrated into the iPod Touch and, not far from now, the new iPads.

Only pictures of the proposed Finger Print Scanner button are from website run by Sonny Dickson. For those that have heard his interviews on TV or have visited his website it's obvious that this is not a real part. When asked if Apple has contacted him about what he is doing he said "NO". If these were real parts I think Apple would have already done something. This guy is operating an advertising hit website making $2000 a month by providing parts that are not necessarily Apples. The more notariety be gets the more hits the bigger his profit
Take what you read on his website with a grain of salt as the credibility is lacking
By the way the 2 iPhone 5s gold and graphite cases had been out for days before he posted those parts on his website

And there's nothing wrong with him profiting. No harm done if we don't take his *leaks* with a grain of salt. Speculation is supposed to be fun. Chillex. :)

Very interesting. If this is right, then it shows starkly how hard doubling down on secrecy really is for Apple. Then there is the whole challenge of lining up partner support for any NFC-based transaction processing. It's unlike Apple not to have this in place before announcing a major new feature. But it's been a long time since they have kept under secret any negotiations with new partners.

I'm still wondering if this will be integrated into the iPod Touch and, not far from now, the new iPads.

It makes sense that they are debuting this with iPhone, since most people carry their smartphones with them everywhere, so making payments with a phone is a logical step.

That's less so the case with the iPod Touch and iPad. The iPad may get a fingerprint sensor one day, but I don't know how useful an iPad would be as a wallet. Maybe on Macs and iPads the sensor will be used only for unlock?

Anyway I agree with your other points. It's really looking like Apple may have hidden this whole thing from everyone and their partners (whether Apple has partnered with card companies, retailers, or carriers) have done a great job keeping quiet.

The gray rings in Apple's invitation to the September 10th event are consistent with a ring around the home button being important for fingerprint sensing (and maybe other functions), as the colored dots are consistent with colorful iPhones to be announced.